High impact strength composition containing isotactic polypropylene, asphalt and elastomer



United States Patent 3,154,508 HIGH llMPACT STRENGTH COMPOSITION CON-TADJING ISOTACTIC POLYPROPYLENE, AS- PT AND ELASTOIVER James B.Clelland, Newtown Square, Pa., assignor to Sun Oil Company,Philadelphia, Pa., a corporation of New Jersey No Drawing. Filed Nov.23, 1960, Ser. No. 71,162

3 Claims. (Cl. 260-285) 3,154,508 Patented Oct. 27, 1964 "ice tage oflow cost, low brittle point, and, surprisingly, a far higher impactstrength than can be obtained by blending an equivalent amount of theelastomer with the polypropylene alone. The amount of polypropylene inthe blend may vary from about 50% to about 80%, the asphalt may varyfrom about 15% to 45%, and the amount of elastomer may be from 5% to25%. Preferably the Weight ratio of asphalt to elastomer is about 2:1,although Weight ratios of from 5:1 to 1:1 may be used with good results.The materials may be blended in any equipment which will produce ahomogeneous product, but preferably a Banbury rubber mill is used.

Physical properties of blends of polypropylene with elastomers alone,with asphalt alone, and with a mixture of asphalt and elastomer are setforth in the following table. The asphalt used had a viscosity of 7870SUS at 210 F.; softening point 100 F., and a penetration at 77 F. of168.

Table l Composition, Weight Percent:

Polypropylene 100 95 9O 85 80 60 Asphalt 4O Butyl Bubber 5 10Ethylene-Propylene Copolymer Properties:

Izod Impa (notched), it. lbs/in 1. 24 1.84 2. 5 3. 76 .89 Brittle Point,C +12 +8 0 9 +10 Yield Strength, 1/min., p.s.i 4, 749 4, 288 3, 840 3,569 2, 082 Heat Distortion, C 37 Composition, Weight Percent:

Polypropylene 51 51 60 70 Asphalt 34 34 25 Butyl RubbeL 15 10 5Ethylene-Propylene Copolymer 15 Properties:

Izod Impact (notched), ft. lbs/in 15. 5 15.0 9.0 4.0 Brittle Point, C 7.5 4. 5 +3 +9 Yield Strength, 1/min., psi. 1, 835 2, 160 2, 350 3,000Heat Distortion, C 35 67 38 41 importantly, must possess a high impactstrength and low brittle point, since soil pipe is subjected to roughhandling during transportation from the Warehouse to the constructionsite. For example, in unloading soil pipe from a truck, it is customaryto throw it from a considerable height to a hard surface, such as apaved road.

It has heretofore been proposed to incorporate an elastomer such asbutyl rubber into isotactic polypropylene in order to improve impact andbrittle point but, while a moderate improvement in properties isobtained, the cost of compositions containing only polypropylene andbutyl rubber is so high that the compositions are not competitive in thesoil pipe field. In the past, also, attempts have been made to lower thecost of plastic compositions comprising polypropylene by blendingpolypropylene with low-cost fillers such as asphalt. Thepolypropyleneasphalt blends may contain up to or so of asphalt, so thatthe price of the composition is competitive in the soil pipe field, butthe brittle point and impact strength of the compositions are about thesame as the properties of unmodified polypropylene, and the compositionsare therefore not fitted for use in applications in which high impactstrength and low brittle point are required.

I have now found that if a combination of asphalt and an elastomer suchas natural rubber, butyl rubber, or an ethylene-propylene copolymer isblended with isotactic polypropylene, the resultant composition has theadvan- As may be observed from the foreoing, the blend of asphalt andpolypropylene alone had a brittle point and impact strength aboutequivalent to the unmodified polypropylene, the blends containingpolypropylene and butyl rubber alone had somewhat improved impactstrength and brittle point, but the blends containing both the elastomerand asphalt had impact strength far higher than could be predicted froma knowledge of the impact properties of blends of polypropylene and anelastomer alone. Thus asphalt alone has little or no effect on impactstrength, and 15 of butyl rubber in polypropylene increases the impactstrength only to 2.5, yet the combination of 15% elastomer and asphaltraises the impact strength to 15 and over. It is not known how theasphalt and elastomer cooperate to achieve this result, but the 1111-expected synergism between the two is evident from the data.

The properties given in the foregoing Table I were obtained as follows:

Izod impact by ASTM D256-54T, Method A.

The invention claimed is: 1. A new composition of matter comprising fromabout 50% to about 80% isotactic polypropylene, about 15% to 45%asphalt, and from about 5% to 25% of an elastomer selected from thegroup consisting of butyl rubber and an ethylene-propylene copolymer,said composition having a tensile strength of at least 1700 p.s.i. andan Izod impact strength of at least 4.

2. The composition according to claim 1 in which the elastomer is butylrubber.

3. The composition according to claim 1 in which the elastorner is anethylene-propylene copolymer.

References Cited in the file of this patent UNITED STATES PATENTSAnderson et a1. Apr. 16, 1940 Skooglund Oct. 13, 1942 Sparks Jan. 25,1944 Thayer Jan. 27, 1959 Sayko Oct. 20, 1959 Carr Dec. 29, 1959 ZappApr. 4, 1961 Gessler et a1. June 5, 1962

1. A NEW COMPOSITION OF MATTER COMPRISING FROM ABOUT 50% TO ABOUT 80%ISOTACTIC POLYPROPRYLENE, ABOUT 15% TO 45% ASPHALT, AND FROM ABOUT 5% TO25% OF AN ELASTOMER SELECTED FROM THE GROUP CONSISTING OF BUTYL RUBBERAND AN ETHYLENE-PROPYLENE COPOLYMER, SAID COMPOSITION HAVING A TENSILESTRENGTH OF AT LEAST 1700 P.S.I. AND AN IZOD IMPACT STRENGTH OF AT LEAST4.